Scheme 3.

Ligand Substituent Effects and Reaction Optimization.^a

^a Conditions: 1 (0.075 mmol), 1 atm O₂, MS 3 Å (20 mg), toluene (0.75 mL), 12 h. Yield determined by ¹H NMR spectroscopy, internal standard = 1,3,5-trimethoxybenzene. Enantiomeric excess deteremined by chiral HPLC (see Supporting Information for details). ^b 5.5 mol % ligand. ^c Without MS 3 Å. ^d 25 °C, 24 h. Isolated yield (0.5 mmol scale).